1. Field of the Invention
The present invention relates to a sustained release pellet suitable for use as an implant in a living being.
2. Description of the Background Art
In many therapeutic, medical and veterinary programs, it is often desirable and/or necessary to provide for the slow release of a beneficial agent to a living being at a controlled rate over a prolonged period of time.
There have been various approaches in attempting to provide a sustained release device which could release a beneficial agent, such as a drug or hormone, at a controlled rate. One method used is to mix the agent with a carrier material that is gradually broken down by body fluids, the agent being released as the carrier disintegrates. Waxes, oils, fats and soluble polymers are some materials that have been used as the carriers in these sytems.
Methods for producing implants wherein a protein is the beneficial agent (active ingredient) and a polymer is the carrier or matrix material, are known in the art. These methods involve either the casting of a dispersion of a protein in a polymer solution followed by slow removal of solvent from the solution at low temperature (e.g., overnight at -60.degree. C.), or by compression molding of a dry mixture of a protein and polymer particles. The former method produces implants with low density (e.g., 0.75 g/cc) and poor mechanical properties, while the latter method requires high polymer loading with concomitant low protein loading.
There remains a need in the art for a process capable of yielding implants with high protein loading good mechanical properties, and which is capable of being carried out at room temperatures.